Why Is My Burner Not Firing Up? Causes And Fixes

Key Takeaways

Five common causes stop a burner from firing up: a switch setting that fails to prove its condition, a dirty pilot nozzle, a flame detector that misses the flame, temperature swings, and worn components.
You can do some troubleshooting yourself but it’s always a good idea to call a burner expert in to check it out, Any unresolved problems can become a safety issue or a bigger problem down the road.

When your burner goes down, it’s all hands on deck to get it running again. The tricky part is, there are a million different reasons why your burner might not be firing up. In this article, our burner experts share the most common causes and what to do about each one.

What Does a Burner Need to Light?

A burner needs spark, fuel, and air at the same time to light. When your burner fails, the first question you should ask is: which of these three are missing from the equation?

Combustion systems go through a specific startup sequence, with specific safety checkpoints that need to be satisfied before moving to the next step. A failure can happen at any point along the sequence.

Here is the typical sequence, from power-on to flame:

Airflow is proven. The combustion blower starts, and a switch confirms it is moving air. Any exhaust fans in the system must also be running.
Low gas pressure is confirmed. A switch verifies gas pressure sits above the low threshold.
High gas pressure is confirmed. A second switch verifies pressure sits below the high limit, which places gas pressure in the correct window.
Safety valves are proven closed. Switches inside the valves report that each one is closed before the sequence continues.
The purge completes. Air alone moves through the chamber for four air changes. In a 10 cubic foot box, that is 40 cubic feet of air.
Flame is proven within 10 seconds. The control opens the gas, fires the spark, and a flame sensor watches. If it sees no flame in 10 seconds, everything shuts down, the control locks out, and someone must reset it manually.

After each lockout, the sequence starts over with a full purge before the next attempt. That purge matters for safety. We have published an account of an auto plant paint room explosion that followed multiple light-off attempts without adequate purge (see how industrial fires and explosions happen). For purge requirements in more depth, read our guide to purging airflow before combustion.

What Are the Most Common Reasons a Burner Is Not Firing Up?

Most no-starts trace to one of five causes, and each has a specific check and fix. The causes below run from the first step of the startup sequence to the last. Weather-related causes (3 and 4) are uncommon, but they explain random failures that seem to happen on some days and but not on others.

Cause 1: A Switch or Valve Setting Fails to Prove Its Condition

What causes it: The flame safeguard control waits for every limit switch to report a good condition before it moves to the next step. Each limit switch is a sensor that confirms one condition, such as air moving or gas pressure in range. Those include the airflow, low gas, high gas, and valve proof-of-closure switches. A switch that is out of adjustment, or a switch on a newly replaced valve or sensor that was never set up, leaves the sequence waiting.

Clues that this might be happening: If the burner stops before the purge or before the spark. A recent valve, switch, or sensor replacement is a strong clue.

The burner stops partway through the startup sequence, either before the purge begins or before the spark fires.
The blower may run and a valve may move, yet nothing advances to the next step and no flame appears.
A valve, switch, or sensor was replaced recently. There’s a chance that the new part’s switch may never have been set up correctly.

How to fix it: Check each switch in sequence order against the electrical prints. Confirm that a replaced component’s settings prove the condition the control is waiting for, then cycle the burner several times to confirm it lights every time.

From the field: One recent service call shows how a single switch setting can stop an entire furnace. A plant went down overnight at about 2 a.m. and stayed down until 9 a.m. In our experience, a plant like this loses $10,000 to $20,000 per hour on the low side.

The maintenance team had already replaced the valve that controls air flow, which gave our technician a direction to look. That valve drives fully open, and a switch inside it then starts the purge timer. On the new valve, the switch was never set up, so the purge timer never started. Our technician adjusted the switch, the purge began, the rest of the sequence ran, and the burner lit. A switch setting on an unfamiliar valve is easy to miss when a team looks after many systems.

Cause 2: A Dirty Pilot Nozzle

This cause applies to pilot-fired burners. If your system lights the main burner directly, skip to Cause 3.

What causes it: A pilot-fired burner lights a small pilot flame first, and that flame then ignites the main burner. Small retention holes ring the pilot nozzle’s large center hole and anchor the base of that flame. Dirt in those holes leaves the flame unstable.

The design is similar to a garden hose nozzle. There is a larger stream in the middle and small streams surrounding it. In combustion, those small streams are what keep the flame steady. With no spray nozzle on the end, a thick stream pours out.

Clues that this might be happening:

The pilot lights, then goes out as the main gas valve opens.
Without clean retention holes, the pilot flame burns only from the center hole.
The flame looks fine until the gas pressure bounces, and then someone has to relight it.

How to fix it: Confirm the pilot has spark, fuel, and air, then inspect the nozzle. Many retention holes run at an angle through the nozzle, so a wire cannot clear them, and replacement is the usual fix. A new nozzle lasts about five years in a normal environment and about three years in a dirty one.

Cause 3: A Flame Detector Misses the Flame

What causes it: The flame safeguard control, the safety controller that runs the startup sequence, relies on a flame sensor to confirm the burner is lit. That sensor is either a flame rod or a flame-sensing eye. If it reports no flame within 10 seconds of the spark, the control shuts everything down and locks out. After an overnight shutdown on a cool, damp morning, moisture can collect on the sensor, so the burner can light while the sensor fails to see the flame.

Clues that this might be happening:

The burner lights, but the control reports no flame and locks out.
It happens on a cool, damp morning after an overnight shutdown.
It may take two or three attempts to start, because the heat from each one dries the sensor a little more.

How to fix it: Reset the control and try again, allowing the full purge each time. Never shorten or skip the purge between attempts. If the problem keeps returning, have a technician check the sensor.

Cause 4: A Fuel-Air Mix Shifts With Temperature

What causes it: Air density changes with temperature. Cold air is denser, so more air enters the burner and your fuel mix can turn lean. Hot air is less dense, so your fuel mix can become rich.

Clues that this might be happening:

A burner that lit reliably all summer fails once temperatures drop to extremes, such as 10 to 30 degrees.
A burner set up in cold weather fails in the first hot weather.

How to fix it: Have a technician check the air-fuel ratio at low fire, 50%, and high fire, then adjust it so the burner runs at the proper ratio.

Cause 5: Worn Components and a Harsh Environment

What causes it: Environment affects burner reliability more than calendar age does. Acids and volatiles corrode components in a chemical plant, and a 110 degree manufacturing floor is harder on equipment than a 70 degree office. Pressure switch diaphragms dry out, and safety valves wear with every open and close cycle. Wires left hanging after poor repairs turn a panel into what our technicians call a “spaghetti factory.” So components wear and need to be replaced on a regular basis.

Clues that this might be happening:

Corrosion on components, especially in chemical plants and other harsh environments.
Aging pressure switches and safety valves.
Loose or hanging wiring in the control panel.
Intermittent start failures with no clear pattern.

How to fix it: Replace worn switches and valves and restore panel wiring. Clean repairs extend a system’s life, and we see 25-year-old systems that still run well.

How the Five Causes Compare

Cause	Typical symptom	Fix
1. Switch or valve setting	Sequence stops before purge or spark	Adjust the switch setting
2. Dirty pilot nozzle	Pilot lights, then goes out as main gas opens	Replace the nozzle
3. Flame detector	Burner lights, control reports no flame	Retry with a full purge; technician check if it recurs
4. Fuel-air shift	Lights in mild weather, fails at extremes	Technician adjusts the air-fuel ratio
5. Wear and environment	Intermittent start failures	Replace worn parts, restore wiring

When Should You Call a Burner Technician?

Calling a technician is always a good idea when your burner fails to fire up. It matters most when the checks above point to a switch, valve, or control you cannot verify against the electrical prints, or when the burner locks out again after a reset. A jumper can get a burner through a start, but it restores operation without identifying why the switch was open.

Safety switches protect the plant from lighting a burner under unsafe conditions, so an open switch is information about the system. We have seen plants where the team knew a jumper on a certain relay would start the burner, yet lacked an explanation for why the relay was open.

Get Your Burner Firing Up Reliably

When your burner is down, every hour counts, and we are committed to getting you back online as soon as possible. Our technicians work out of service locations in St. Louis, Kansas City, and Denver, so experienced help is close to your plant. We also keep a large inventory of combustion parts on hand to make repairs fast.

Request service and our team will work to get your burner firing again.